1992 Volume 85 Issue 12 Pages 1967-1973
In adult humans, hypothyroidism has been associated with a reduced sense of smell. There are few reports on the effect of hypothyroidism on the sense of smell in adult animals. We examined whether hypothyroidism abolishes the sense of smell in adult mice and examined the changes of the olfactory epithelium. Hypothyroidism was produced in adult mice by addition of thiamazole to their drinking water or intra-peritoneal injection. The olfaction of mice was estimated by successful recording of behavioral task, using cycloheximide, which has been commonly used as a repellent in rodents. The sense of smell was tested before, during, and after thiamazole treatment. Thyroid function was assessed by radioimmunoassay of blood serum for free thyroxine. The mice were killed after treatment and the olfactory epithelium was studied at the light microscopic level to determine the effects of thiamazole treatment.
Mice given 0.01% thiamazole in the drinking water for 100 days were not hyposmic. The control mice given tap water to drink for 100 days maintained their sense of smelll. Mice given daily intra-peritoneal injection of 0.5 mg thiamazole for 100 days were not hyposmic. Daily i. p. injection of 1.5mg thiamazole to the mice for 20 days attenuated their sense of smell. By contrast, the control mice, given daily i. p. injection of 0.1ml normal saline were normosmic. In the olfactory epithelium of the hypothyroid and hyposmic mouse, the structures composed of basal cells, olfactory cells, and supporting cells were preserved. However, a marked decrease was observed in the number of olfactory cells. These findings indicate that hypothyroidism produces olfactory disturbance in mice and injures the olfactory receptor neurons.
